With Monday’s engine tests at Boscombe Down stopped due to intake-induced surging in ThrustSSC’s two Spey jet engines, the team spent Tuesday diagnosing and discussing the problem - working closely with Rolls-Royce (the manufacturers of the engines) and the intake designer. It was clear that the underlying problem was that while the car was stationary insufficient air could reach the engines at the high power outputs being tested. During operations on the Farnborough runway and in the deserts this would not be a problem - the car would never start on full-power, and above 100 mph or thereabouts the forward motion would ensure sufficient air was rammed into the intakes.
However, the team was determined to able to test the engines at maximum power while stationary - which was crucial to testing the car’s systems and the ability of the rear fuselage to withstand the extreme environmental conditions of a fully reheated Spey’s exhaust. Vortexes around the intakes caused by air from behind the lip coming forward and meeting air coming back from in front of the car was one suspected culprit. Rather than modify the car unnecessarily, the team decided to test this theory first, so on Wednesday (14th August) they took ThrustSSC back out onto the runway at Farnborough, tied the car down and ran the engines with a sheet of water on the tarmac in front to show up the air movements.
Vortexes were clearly seen, so ‘vortex mats’ were placed on the ground in front of the car to prevent them forming and the engines started again. The mats are designed to control airflow to prevent vortices forming - and they worked. Although not convinced this was the cause of their difficulties, the engine team were sufficiently encouraged to warrant a return to DTEO Boscombe Down for further tests to diagnose the problem - this time with a Rolls-Royce expert to assist with the studies.
Another early start was planned for Thursday. The superb Grayston White and Sparrow crane arrived from its Colnbrook depot at the crack of dawn, and the two trailers were re-loaded with ThrustSSC, the now-invaluable Merlo forklift and dolly - and the vortex mats. The vehicles departed for Wiltshire and arrived in good time - except for the crane. It had suffered a blowout on the A303! Grayston White and Sparrow pulled out all the stops and after a tyre-fitter and replacement tyre were rushed up from Southampton, the crane was again underway. By mid-afternoon ThrustSSC was once again in position and tied down in the test cell - this time with the vortex mats in place too.
The warm greeting and hospitality at Boscombe was just as good as on the team’s first visit on Monday. Sadly the young lady from Health and Safety was not around this time - tasked on our previous visit with checking that all the visitors were briefed on the safety aspects of running jet engines, she had amused us all with one of the best quotes of the project to date: "And that Mr. Richard Noble who has just arrived - does he need a safety briefing or does he know something about jet-cars?". Glynne Bowsher pointed out that in all fairness, she was probably still at school in 1983...
It was an even hotter day than Monday - and this time many of the team had wisely brought hats to go with their all-important ear defenders. The firemen standing by hosed down the vortex mats to indicate airflow around the intakes, the ‘Palouste’ was started, popping loudly as it built up speed, and the signal was given by Al Harkness: "Air on to the left-hand engine". With a whine the turbines started, and as the engine fired, the throttles were advanced until it was running at 95% of maximum revolutions. With the right-hand engine stationary, the load-cell was still reading well over 10,000 pounds of thrust. The engine stabilised at 95% with no vortices evident. After holding at that setting, it then surged again and was quickly shut down.
Al, Paul Remfrey, Steve Wiltshire, Pete Ross and the team gathered and went over the test - the mats had made a difference, but not as much as was needed. It was obvious that they had to know in detail what was happening around the intakes at very high power settings while the car was not moving. The left-hand engine was started again and a wind-tunnel smoke wand was used to study the airflow all around the intake.
Photographs and video were also taken, and having got all the data they needed, the team called the crane into action again, loaded up the car and equipment and returned to DRA, Farnborough. Two major and costly solutions remained - one involving surgery to the car. The team decided to evaluate the alternatives overnight, and met this morning to agree the next move. The engineering aspects of these solutions are now being worked on around the clock, and it is hoped that the next visit to Boscombe Down will enable to team to finally witness the ‘dancing diamonds’ in the twin 30 foot-long reheat flames.
We will of course continue to bring you the news as it happens!
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